A condensing unit is a key component of a typical residential split air-conditioning and heat pump system, wherein the condensing unit is primarily comprised of the compressor, the outdoor coil, fan and connections. During the installation of such a system, the outdoor unit is connected to two lines (high and low side) that convey refrigerant medium to and from the indoor coil and expansion device. These two connections, on the condensing unit, are made at the liquid (high side) and the suction (low side) service valves. Since the suction side service valve conveys gaseous refrigerant medium, it is a substantially larger valve than the liquid side service valve that conveys the liquid refrigerant medium. After the necessary braze connection is made, these lines, between the indoor and outdoor coils, are evacuated of air through charge ports located on the service valves. Thereafter, the shut-off valves are opened thus allowing pre-charged refrigerant medium to flow from the condensing unit throughout the noted system.
The main functions of a typical state of the air-conditioning service valve are to:                1. Retain pre-charged refrigerant medium in the condensing unit before installation;        2. Provide a shut-off for the possibility of a “pump-down”. During the “pump-down” process, the liquid service valve is closed and the compressor is turned on so that the refrigerant medium is conveyed to and stored in the condensing unit. Once this process is completed, the suction line service valve is closed. In this way the indoor coil, expansion device, and connecting lines can be accessed without removing the refrigerant medium from the system; and        3. Provide a service port via which a hose connection can be used to evacuate the refrigerant medium or monitor the system pressure for diagnostic purposes.        
A typical state of the art air-conditioning service valve exhibits a generally “Z” flow path inherent in a front seat valve design which, however, is not conducive to a low pressure drop. While a pressure drop, in the liquid line of the system, is not usually detrimental to system performance, a suction line pressure drop causes a definite decrease in system efficiency. Therefore, the suction side service valve design has developed a design stratification whereby the flow path and subsequent pressure drop associated with this valve have become important features. Some condensing unit manufacturers utilize a ball-style valve that exhibits a large straight flow path, but the cost of this valve is substantially higher than that of the usual front seat valve. Not surprisingly, many manufacturers prefer the lower cost of the usual front seat valve for the suction service valve application and will compensate for the added pressure drop, and its associated efficiency losses, via design changes in other areas of the system. Another benefit of the ball-style valve is the ease of actuation of the valve stem in that turning the ball valve stem but one quarter turn will cause the valve to open or close, while the front seat style valve requires multiple complete rotations of its valve stem to either open or close the valve.
The construction of the present invention employs a valve style that is presently not used in residential air-conditioning and heat pump applications, namely a plug-style valve. The use of a plug valve is advantageous in the suction side service valve application since the flow path thereof is straight through the valve body, a key characteristic in pressure drop considerations. In addition, the through-hole in the stem of the plug valve can readily be sized for reduced pressure drop, and a plug-style valve requires only a minimal actuation motion, similar to that of a ball valve.
One of the challenges encountered in the state of the art plug valves, such as the one set forth in U.S. Pat. No. 5,234,193, to Neal Jr., also assigned to the assignee of the present invention, is the difficulty in retaining the circular seal on the side of the valve's stem. The noted patent structure uses a press-in-place custom seal that can be difficult to assemble. Other plug-type valves, such as the one shown in U.S. Pat. No. 4,262,880, to Danko, et al., rely on an O-ring that is held in the side of the stem by the dovetail nature of its receiving gland, whereas the present invention uses a serpentine gland that permits the O-ring to be stretched substantially around the valve's stem as an improved means to retain the seal or O-ring in its groove or gland.
The previously-noted prior art plug valves use a seal on the side of the valve stem to seal off the valves' through holes when the valves are closed. When the valves are opened, this seal is not utilized, and a second O-ring around the top of the valve becomes the primary seal against leakage between the stem and the valve body. The unique shape of the present invention serpentine gland allows the O-ring located therein to be so positioned that it functions as the primary seal against stem/body leakage when the valve is in the open position. In the present invention, the other O-ring around the top of the stem is the primary seal only when the valve is closed and a secondary seal when the valve is open. This is of particular importance since an air-conditioning service valve requires that the valve be in its open position almost exclusively after the system has been installed. In addition, the thus double O-ring seal, in the open position, allows for the use of a soft seal, not the customary metal-to-metal seal.
A further difficulty faced by the state of the art plug valves is the possibility of the seal being damaged by the edge formed by the inside diameter of the valve body and the valve's lateral through holes since the seal does contact this edge during the actuation of the valve stem. Furthermore, the seal can also contact the noted edges during the initial assembly of the valve if, at that time, the seal is not positioned away from the valve's through holes. In the structure of the present invention, the location of the serpentine gland portion that extends around the top of the valve stem allows for the serpentine O-ring to be located away from these edges during the assembly step.
The patent literature includes a plurality of plug-type valve constructions including: U.S. Pat. No. 3,186,437 to Buono that includes a pointer that indicates the position of a valve passage within the valve body; U.S. Pat. No. 3,783,890 to Wurzburger, U.S. Pat. No. 3,802,457 also to Wurzburger, U.S. Pat. No. 5,219,149 to Combeau, and U.S. Pat. No. 5,372,158 to Berfield, all of which pertain to plug-type valves that employ varying styles of serpentine seals; while U.S. Pat. No. 6,216,473 B1 pertains to an air-conditioning service valve structure that is similar to that of the present invention only in that it also utilizes a service port. In this structure, specifically as shown in FIG. 7, fluid flows to a recovery circuit via fluid recovery inlet port 1105A, but fluid can still flow, albeit via leakage, from inlet 1102A to outlet 1102B, since peripheral seals 1110 only prevent horizontal or lateral leakage when inlet 1102A is aligned with outlet 1102B as shown in FIG. 8, but not peripheral leakage in the FIG. 7 position. However, none of these prior art constructions teach or suggest the unique valve structure of the present invention.